The present invention relates to methods and computer program products for determining whether subjects are at risk for developing Type 2 diabetes and other insulin resistance disorders.
Type 2 diabetes, sometimes referred to as adult-onset or non-insulin dependent diabetes mellitus (NIDDM), affects approximately 15 million people in the United States alone. Additionally, approximately 21 million Americans have impaired glucose tolerance or xe2x80x9cborderline diabetesxe2x80x9d (characterized by high blood sugar levels not high enough to be considered diabetic). Both Type 2 diabetes and borderline diabetes are related to insulin resistance, a condition where the body fails to respond normally to insulin. Insulin resistance is associated with other health problems, including high blood pressure and heart disease. If unchecked, insulin resistance may actually develop into Type 2 diabetes. Type 2 diabetes is associated with a two- to fourfold excess risk of coronary heart disease, and diabetic patients are at an increased risk for morbidity and mortality associated with cardiovascular disease.
Type 2 diabetes has been traditionally diagnosed by the detection of elevated levels of glucose (sugar) in the blood (hyperglycemia). While hyperglycemia is a strong indicator of diabetes, it is a very late stage development in the chain of events that lead from insulin resistance to full-blown diabetes. Accordingly, it would be desirable to have a way of identifying whether or not a subject is at risk for developing Type 2 diabetes (i.e., is predisposed to the condition) prior to the development of the classic symptoms, such as hyperglycemia. Earlier detection of indicators of the disease (e.g., detection of an increase in glucose levels prior to the levels reaching an elevation high enough to be considered hyperglycemia) may lead to more effective treatment of the disease, if not actual prevention of the onset of the disease.
The diagnosis of cardiovascular disorders such as coronary heart disease (CHD) is routinely accomplished by the measurement and analysis of blood cholesterol levels of subjects suspected of having such disorders. In such analyses, total serum cholesterol (TC) is measured, as well as plasma triglyceride levels (TG). Additionally, levels of the major lipoprotein constituents or classes of cholesterol are often measured. These major lipoprotein constituents include low density lipoprotein (LDL), high-density lipoprotein (HDL), and very low-density lipoprotein (VLDL). The major lipoprotein constituents may be further subdivided into subclasses based on further refinement of particle densities. Krauss et al, J. Lipid Research 23, 97-104 (1982); Atger et al., Clinical Chemistry 37, 1149-1152 (1991). A subclass of lipoprotein particles comprises particles which have common physical properties, such as density. Subclasses distinguished upon density may be considered as a subclass of the class of lipoprotein which contains particles of the subclasses"" density.
U.S. Pat. No. 4,933,844 to Otvos describes the use of proton nuclear magnetic resonance (1H NMR) spectroscopy to analyze blood plasma and determine the concentration of the major lipoprotein constituents in a blood plasma sample. U.S. Pat. No. 5,343,389 to Otvos describes the use of 1H NMR spectroscopy to analyze blood plasma or blood serum for concentrations of lipoprotein subclasses. The methods described in these patents rely on the fact that 1H NMR spectra of human blood plasma contain two prominent peaks centered at approximately 1.2 and 0.8 ppm (relative to a chemical shift standard). These peaks arise from methylene (CH2) and methyl (CH3) protons, respectively, of plasma lipids. Each of these peaks is heterogeneous in nature, consisting of overlapping resonances from protons of the several chemically distinct classes of lipids present in plasma: triglycerides; cholesterol; cholesterol esters; and phospholipids. These lipids are packaged together into the three major classes of lipoprotein particles described above, which differ in density and in the proportions of lipids which they contain. The heterogeneity of these plasma signals is reflected by their complex lineshapes, which vary from person to person owing to variations of the plasma concentrations of the different lipoprotein particles, each of which has its own characteristically different NMR spectral properties. Additionally, lipoprotein subclasses of the major lipoprotein classes or constituents exhibit NMR-measurable properties that are distinct from other subclasses. The NMR properties of one subclass may be distinct in a number of ways, such as chemical shift or lineshape variations, which make the subclass distinguishable from other subclasses.
In view of the foregoing, it is an object of the present invention to provide a more reliable method for determining if a subject is at risk for developing Type 2 diabetes.
It is another object of the present invention to provide a more accurate and/or reliable method for determining if a subject is at risk for developing insulin resistance syndrome.
It is another object of the present invention to provide an improved method for determining if a subject is suffering from insulin resistance syndrome.
It is still another object of the present invention to provide an improved method for evaluating the efficacy of treatment of a subject suffering from Type 2 diabetes.
It is additionally another object of the invention to provide a method of determining the glucose concentration in a blood plasma or blood serum sample (xe2x80x9cblood glucose levelsxe2x80x9d), and further to be able to determine blood glucose levels at sub-hyperglycemic levels.
In order to minimize the necessity of performing numerous, expensive and duplicative tests for determining risk for Type 2 diabetes and disorders of insulin resistance, it is still another object of the invention to provide a method of determining the glucose concentration in a blood plasma or blood serum sample concurrently with determining other lipid-based risk factors for Type 2 diabetes or disorders of insulin resistance.
It is an additional object of the present invention to provide an economical way of screening a subject""s blood plasma sample to determine the subject""s risk of developing Type 2 diabetes.
It is yet another object of the present invention to provide a computer program product for determining whether a subject is at risk for developing Type 2 diabetes.
These and other objects of the present invention are provided by a method for identifying a patient with an increased risk of developing Type 2 diabetes by analyzing the patient""s NMR lipoprotein constituent measurements. Additionally, the risk of the patient developing Type 2 diabetes may further be determined by analyzing the patient""s blood glucose levels with NMR spectral analysis. The ability to analyze a patient""s blood glucose levels by NMR analysis provides several advantages in that it allows for a blood glucose measurement to be taken concurrently with a patient""s lipoprotein constituent measurements, thus avoiding the need for multiple testing events for determining risk for Type 2 diabetes. Additionally, the sensitivity of the NMR-based blood glucose test performed in conjunction with an NMR-based blood lipoprotein test provides an earlier detection of risk for developing Type 2 diabetes. A moderately elevated blood glucose level in the absence of other indicators of risk for developing the disease may not be sufficient to alert a health care provider or a patient that an increased risk of developing the disorder is present. However, a moderately elevated blood glucose level, as detected by the NMR-based methods of the present invention, in conjunction with the presence of other risk factors identified by the NMR-based blood lipoprotein analysis of the present invention, enables a practitioner to determine the risk of developing disorder prior to the onset of the full-blown disease.
In particular, a first aspect of the present invention is a method of determining if a subject is at risk of developing Type 2 diabetes by analyzing a blood sample collected from the subject with NMR spectral analysis. A blood sample, such as blood plasma or blood serum, is collected from a subject. The subject may be a subject that is suspected of being at risk of developing Type 2 diabetes, or may be a subject undergoing a lipoprotein analysis for any other reason (e.g., as a standard screening for cardiovascular disease). The subject may be exhibiting symptoms of Type 2 diabetes, but may alternatively be asymptomatic. The blood sample is then analyzed by NMR spectral analysis.
This NMR-based analysis includes determining a lipoprotein specific constituent identified as being an independently predictive risk factor (in isolation of the other constituent values) and determining a risk associated with a combination of certain of the constituent measurement values. Preferably, the combination method identifies whether the patient""s results provide a positive match with key NMR-measured factors. One factor is the determination of the presence of diabetic dyslipidemia (i.e., a clustering of predetermined moderate, borderline, or positive NMR lipoprotein subclass or constituent-based risk values). An additional factor is the detection of at least a moderately elevated NMR-measured glucose level. Advantageously, this type of risk analysis allows for a determination of blood glucose levels prior to an increase in blood glucose levels sufficient to qualify as hyperglycemia (i.e., a moderately elevated blood glucose level that is potentially indicative of Type 2 diabetes can be detected).
Another aspect of the present invention is directed to a method for assessing a patient""s risk of developing Type 2 diabetes based on NMR-measured lipoprotein-based information. The method includes generating NMR-based lipoprotein measurement values for a patient""s blood plasma or serum sample. The NMR-based lipoprotein measurement values comprise at least one lipoprotein constituent value, but preferably comprise a plurality of lipoprotein constituent values. In a preferred embodiment, the method also includes generating an NMR-based glucose concentration measurement value for a patient""s blood serum or blood plasma sample. The plurality of NMR-based lipoprotein constituent values are compared to predetermined test criteria to determine the presence of diabetic dyslipidemia. The NMR-based glucose concentration measurement value is compared to a predetermined test criteria to determine the presence of an increased risk for Type 2 diabetes. A patient""s risk of Type 2 diabetes may be assessed based on the presence (or absence) of diabetic dyslipidemia, and on the presence or absence of at least moderately elevated glucose levels.
In a preferred embodiment, the NMR-based lipoprotein constituent measured values include the values associated with LDL size, LDL particles, large HDL cholesterol, and large VLDL triglyceride.
An additional aspect of the present invention is an NMR-based method for measuring the glucose concentration of blood. In this method, an NMR reference data spectrum corresponding to glucose in a reference blood plasma or serum sample or specimen is acquired and stored in computer memory. A reference coefficient is assigned to one glucose signal or group of glucose signals (xe2x80x9creference glucose lineshapexe2x80x9d) in the reference spectrum, the value of which is based on the glucose concentration of that reference specimen determined by an independent chemical glucose measurement. An NMR spectrum of a patient""s blood plasma or serum specimen is acquired at some later time under measurement conditions (substantially) identical to those used to obtain the glucose reference spectrum and stored in computer memory. The reference glucose lineshape is compared with the same glucose signal or group of signals in the patient spectrum (xe2x80x9cpatient glucose lineshapexe2x80x9d). A calculation is then performed which determines the scaling factor needed to adjust the amplitude of the reference glucose lineshape to give the best match with the patient glucose lineshape. This scaling factor is multiplied by the reference coefficient to give the concentration of glucose in the patient blood plasma or serum specimen.
A further aspect of the present invention is a computer program product for personalized NMR-based risk assessment for Type 2 diabetes. The computer program product comprises a computer readable storage medium having computer readable program code means embodied in the medium. The computer-readable program code means comprising computer readable program code means for generating NMR-based lipoprotein measurement values and NMR-based glucose measurement values for a patient""s blood sample, the lipoprotein measurement values including at least one subclass variable value. The computer program product also includes computer readable program code means for comparing the at least one patient lipoprotein subclass variable value with predetermined test criteria for determining whether the at least one subclass variable value is associated with a higher or lower risk of developing Type 2 diabetes and computer readable program code means for identifying, for the at least one measured subclass variable value, the corresponding risk level associated with Type 2 diabetes. The computer program product also includes computer readable program code means for providing a risk analysis portion positioned adjacent to the measured lipoprotein values, the risk analysis portion displaying information corresponding to higher and lower risk for Type 2 diabetes. The measured value is visually enhanced in the risk analysis portion to indicate visually the level of risk associated therewith, thereby providing a contemporaneous reference guideline for interpretation of the measured value. The computer program product additionally includes computer readable program code means for comparing a plurality of the NMR-based lipoprotein measurement values to predetermined test criteria to determine the presence of diabetic dyslipidemia. The computer program product also preferably includes computer readable program code means for comparing NMR-based glucose measurement values to predetermined test criteria to determine the presence of elevated blood glucose levels.
In a preferred embodiment, the NMR-based lipoprotein values include the subclass values associated with LDL size, LDL particles, large HDL cholesterol, and large VLDL triglyceride, and the computer program product further comprises computer readable program code means for presenting the lipoprotein measurement values such that each of the lipoprotein measurement values is substantially aligned.
Preferably, for the methods and computer program products described herein, the NMR-measured values include: (a) the LDL size and the concentrations of LDL particles, large HDL cholesterol, and large VLDL triglyceride; and (b) the measured blood glucose level.
The present invention is advantageous because the method described above can accurately and reliably indicate whether a subject is at risk of developing Type 2 diabetes or another insulin resistance disorder, such as insulin resistance syndrome. The method provides advantages over the conventional testing methods for Type 2 diabetes and other insulin resistance disorders in that it can provide an indication of increased risk for the disease prior to the development of symptoms of the disease, such as a blood glucose level high enough to be considered hyperglycemia. By the time these symptoms can be detected with conventional methods, the disorder of Type 2 diabetes (or other insulin resistance disorder) has already progressed to an advanced stage. The NMR-based methods of the present invention can indicate increased risk of developing Type 2 diabetes earlier in the development of disease (i.e., prior to symptom development) because (1) risk factors assessed by the NMR-based lipoprotein analysis provide early indication of disease; and (2) the NMR-based glucose analysis provides for determination of increased glucose levels that are sub-hyperglycemic.
The detection of sub-hyperglycemic glucose levels in the absence of other indicators of risk for developing Type 2 diabetes may not be sufficient to alert the health care provider of a patient that the patient is at risk of developing the disorder. The detection of a sub-hyperglycemic glucose level, made concurrently with the detection of other indicators of risk, however, may allow the health care provider the opportunity for intervention prior to the development of the symptoms of Type 2 diabetes (i.e., hyperglycemic blood glucose levels). The present invention thus facilitates early detection of risk for developing Type 2 diabetes in that an NMR-based test for blood glucose levels may be routinely performed concurrently with an NMR-based test or screen for widely ordered tests typically used to assess coronary heart disease-based (CHD-based) blood lipoprotein values, thus avoiding the additional expense and inconvenience of multiple testing events. The routine screening for those at risk for developing Type 2 diabetes can advantageously facilitate a reduction in the number of individuals advancing into the full-blown disease, thereby providing earlier intervention and potential prevention of the progression into the incurable phase of the disease. The early detection of the disposition for the disorder provided by the present invention thus allows subjects diagnosed as being at risk to begin appropriate treatment or lifestyle changes at an earlier point in time. This early detection is advantageous in that it may lessen the severity of the disease as it progresses, if not actually prevent the onset of the disease. The method of the present invention may also advantageously be incorporated into standard lipoprotein screenings for, e.g., cardiovascular disease.
As described herein, additional aspects of the present invention include methods for determining whether a subject is at risk for developing insulin resistance syndrome (also referred to as Syndrome X). Further aspects of the present invention include methods for determining whether a subject is already suffering from insulin resistance syndrome or another disorder of insulin resistance. In these and other methods of the invention, a blood sample is collected from a subject and analyzed by NMR lineshape spectral analysis as described above. In particular, NMR-based lipoprotein values such as the subclass values associated with LDL size, LDL particles, large HDL cholesterol, and large VLDL triglyceride are measured and compared with predetermined test criteria. The satisfaction of specific test criteria for the relationships between the reference parameters and the measured parameters indicates that the subjects are at risk of developing insulin resistance syndrome, or are in fact suffering from insulin resistance syndrome.
An additional aspect of the invention is a method of evaluating the efficacy of treatment of a subject undergoing treatment for Type 2 diabetes or another insulin resistance disorder. A baseline profile of at least one lipoprotein subclass of the subject undergoing treatment for Type 2 diabetes or another insulin resistance disorder is obtained. This profile is obtained by collecting a blood sample from the subject and analyzing the sample by NMR spectral analysis as described above. This baseline profile may be obtained before the subject has actually commenced treatment for the insulin resistance disorder, or may be obtained after the treatment has begun. A second profile of at least one lipoprotein subclass of the patient undergoing treatment for Type 2 diabetes or another insulin resistance disorder is obtained at a time later than the baseline profile. The second profile is obtained in essentially the same manner as the baseline profile, described above. The baseline profile and the second profile are then compared. The difference between the baseline profile and the second profile provides an indication of the efficacy of treatment for Type 2 diabetes or other disorder of insulin resistance in the subject.
The foregoing and other objects and aspects of the invention are explained in further detail herein.